Abstract
Maladaptive impulsivity is a core symptom in various psychiatric disorders. However, there is only limited evidence available on whether different measures of impulsivity represent largely unrelated aspects or a unitary construct. In a cross-species translational study, thirty rats were trained in impulsive choice (delayed reward task) and impulsive action (five-choice serial reaction time task) paradigms. The correlation between those measures was assessed during baseline performance and after pharmacological manipulations with the psychostimulant amphetamine and the norepinephrine reuptake inhibitor atomoxetine. In parallel, to validate the animal data, 101 human subjects performed analogous measures of impulsive choice (delay discounting task, DDT) and impulsive action (immediate and delayed memory task, IMT/DMT). Moreover, all subjects completed the Stop Signal Task (SST, as an additional measure of impulsive action) and filled out the Barratt impulsiveness scale (BIS-11). Correlations between DDT and IMT/DMT were determined and a principal component analysis was performed on all human measures of impulsivity. In both rats and humans measures of impulsive choice and impulsive action did not correlate. In rats the within-subject pharmacological effects of amphetamine and atomoxetine did not correlate between tasks, suggesting distinct underlying neural correlates. Furthermore, in humans, principal component analysis identified three independent factors: (1) self-reported impulsivity (BIS-11); (2) impulsive action (IMT/DMT and SST); (3) impulsive choice (DDT). This is the first study directly comparing aspects of impulsivity using a cross-species translational approach. The present data reveal the non-unitary nature of impulsivity on a behavioral and pharmacological level. Collectively, this warrants a stronger focus on the relative contribution of distinct forms of impulsivity in psychopathology.
Highlights
Impulsivity is a hallmark and common feature in various psychiatric disorders, including substance use disorder, attention deficit hyperactivity disorder (ADHD), conduct disorder, bipolar disorder, pathological gambling and personality disorders [1]
There was no correlation between impulsive action, defined by the number of premature responses and impulsive choice, defined by the indifference point [r(22) = 2.22, ns] or log k-value [r(22) = .09, ns]
In the Delayed Reward Task (DRT), compared to vehicle, AMP caused a decrease in impulsive choice behavior, reflected in an increased preference for the large delayed reward over increasing delays [drug*delay: F(4,84) = 5.84, p,0.001; delays T(21) = 0: .037, 40: 22.00, ns, 5: 23.96, 10: 23.77, 20: 22.38, p,0.05]
Summary
Impulsivity is a hallmark and common feature in various psychiatric disorders, including substance use disorder, attention deficit hyperactivity disorder (ADHD), conduct disorder, bipolar disorder, pathological gambling and personality disorders [1]. Impulsivity can be broadly defined as behavioral actions without adequate forethought, there is growing evidence that impulsivity is no unitary construct, but rather is dissociable into different aspects reflecting distinct underlying cognitive, emotional, and neural processes [2]. Detailed research on the relationship between various aspects of impulsivity is still scarce. Two widely recognized behavioral phenomena of impulsivity are impulsive choice and impulsive action. Impulsive choice is oftentimes operationalized by impulsive decisions resulting from a distorted evaluation of delayed consequences of behavior and an increased preference for (smaller) immediate rewards over more beneficial delayed rewards. Impulsive action reflects the failure to inhibit an inappropriate response to prepotent stimuli [2,3,4]
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